Abstract With the development of Spin-Exchange Relaxation Free (SERF) atomic magnetometers, human weak magnetic measurement has become a hot research direction in the medical field. Cardio-cerebromagnetic monitoring is a new medical detection method in the medical field. Array magnetometer is the core device of cardio-cerebromagnetic accurate monitoring. The volume and accuracy of the array magnetometer directly determine the wearability and sensitivity of the device, and the laser beam splitting system has a great influence on its accuracy and volume. Because the diffraction beam splitting method has the advantages of high beam splitting efficiency, good beam performance consistency, small space occupation, etc., it is suitable for the laser beam splitting module of array magnetometer, which does not reduce the accuracy while reducing the volume. In this paper, we innovatively apply the diffraction beam splitting scheme to the laser beam splitting module of the array magnetometer, with the goal of miniaturizing the integration of the beam splitting module and improving the output accuracy of the array magnetometer. The design and fabrication of a high-performance diffraction beam splitter applied to the beam splitting system of the SERF atomic magnetometer, as well as the output beam quality and power balance of multiple laser beams, ensure the detection accuracy of the array magnetometer. It is important to carry out related studies of laser beam splitter technology for magnetometer development.
Abstract With the development of Spin-Exchange Relaxation Free (SERF) atomic magnetometers, human weak magnetic measurement has become a hot research direction in the medical field. Cardio-cerebromagnetic monitoring is a new medical detection method in the medical field. Array magnetometer is the core device of cardio-cerebromagnetic accurate monitoring. The volume and accuracy of the array magnetometer directly determine the wearability and sensitivity of the device, and the laser beam splitting system has a great influence on its accuracy and volume. Because the diffraction beam splitting method has the advantages of high beam splitting efficiency, good beam performance consistency, small space occupation, etc., it is suitable for the laser beam splitting module of array magnetometer, which does not reduce the accuracy while reducing the volume. In this paper, we innovatively apply the diffraction beam splitting scheme to the laser beam splitting module of the array magnetometer, with the goal of miniaturizing the integration of the beam splitting module and improving the output accuracy of the array magnetometer. The design and fabrication of a high-performance diffraction beam splitter applied to the beam splitting system of the SERF atomic magnetometer, as well as the output beam quality and power balance of multiple laser beams, ensure the detection accuracy of the array magnetometer. It is important to carry out related studies of laser beam splitter technology for magnetometer development.
Atomic magnetometers with magnetic field modulation have emerged as pivotal sensors for biomagnetic measurements. However, challenges such as crosstalk between adjacent modulation fields and the complexity of signal circuitry become increasingly serious in the development of array-based equipment with the magnetometers, especially in the miniaturized atomic magnetometer. This paper proposes an all-optical, fully integrated fiber-coupled atomic magnetometer that employs pump beam modulation. A miniaturized atomic magnetometer with a volume of 10 cm³ has been designed, incorporating an active measurement area of 3 × 3 × 3 mm3. The magnetometer operates in the spinexchange relaxation-free (SERF) regime with an 87Rb vapor cell. An amplitude-modulated pump beam directly modulates the rubidium atomic ensembles, rather than the magnetic field modulation. The optical rotation angle is detected by an unmodulated probe beam oriented orthogonally to the pump beam. In light of the discontinuous pumping characteristics, we developed a modified theoretical model to clarify the output response of the proposed atomic magnetometer. The experimental results demonstrate that the new design achieves the same sensitivity as conventional magnetometer configurations with a smaller volume and without crosstalk of the magnetic field. This research highlights the significant potential for advancing the development of highly sensitive, miniaturized atomic magnetometers, making them particularly suitable for applications in magnetocardiography (MCG) and magnetoencephalography (MEG).
Ultraweak magnetic field measurement, as one of the quantum precision measurement techniques, holds important significance in the forefront of explorations in physics and advanced medical technologies. The atomic magnetometer, serving as a typical instrument for measuring extremely weak magnetic fields, utilizes the Larmor precession frequency of electrons in alkali metal atoms to quantify magnetic field magnitudes at subfemtotesla levels. Additionally, atomic magnetometers boast advantages such as high sensitivity, miniaturization and high spatial resolution. Hence, arrays of atomic magnetometer sensors have become a reliable solution for measuring ultraweak magnetic fields in spatial dimensions. This paper proposes an ultracompact and highly sensitive atomic magnetometer array integrated structure via a highly stable polarization volume grating (PVG)-based waveguide structure for beam splitting. Instead of the traditional four polarizing beam splitters and polarizors, the structure integrates parallel beam splitting and polarization conversion functions using PVGs, which are then incorporated into an ultracompact atomic magnetometer array. This integration enables high sensitivity magnetic field measurements in four channels. The light separated by the structure exhibits power fluctuations along a single polarization axis below 0.2% during a 30 min period. The overall volume of the proposed integrated structure is approximately 0.6 cm 3, representing at least an order of magnitude reduction compared to other spatial optical atomic magnetometer array structures. The final validation demonstrates the system can measure magnetic fields on the order of femtotesla, with an average sensitivity of 16.1 fT/Hz 1/2 . This approach holds significant potential for applications in quantum precision sensing, high resolution medical imaging, and biological science exploration.
High sensitive SERF(spin-exchange-relaxation-free) atomic magnetometers play an important role in many fields including geophysical mapping, space science, nuclear magnetic resonance, health care and perimeter and remote monitoring. This paper presents a novel approach for the system integration of a SERF atomic magnetometer. First of all, Rb vapor cell integrated with micro heater and Helmholtz coils was selected as physic part of the system and the vapor cell was characterized by pressure broadening effect to analyze nitrogen buffer gas pressure in the vapor cell. Then optical module including laser, micro-lens to collimate light beam emitting from the laser, quarter-wave plate to circularly polarize laser beam was taken as optical pumping and probing source simultaneously, and the interaction of circularly polarized laser beam with rubidium atoms was detected by silicon PIN photo-detectors. At last, Laser module, physics part of the system and silicon PIN photo-detector were integrated on a glass wafer substrate benefiting from the characteristics of non-magnetic material and good flatness, based on the integrated SERF atomic magnetometer, weak magnetic field could be measured. Results demonstrate that the SERF atomic magnetometer is integrated successfully and could be used for the detection of weak magnetic field.
The ultra-sensitivity magnetometer plays an important role in fundamental physics and applications, including magnetoencephalography (MEG) and magnetocardiography (MCG). The spin-exchange relaxation-free (SERF) atomic magnetometer (AM) has great sensitivity but is limited by the relatively complicated dual-beam structure for application, leading to the development of the compact AM based on one single laser beam. Compared with the single-beam optically pumped magnetometer (OPM) detecting the absorption of the circularly polarized beam, the SERF AM based on an elliptically polarized single beam detecting the optical rotation angle of polarization has a better response, lower laser power, and no need for signal modulation or demodulation. Here, we would like to report an elliptically-polarized single-beam SERF AM enhanced by reflecting the probe beam, increasing the light-atom interaction. Moreover, unlike the previous reflecting AM using the beam splitter, we used a D-shape mirror to extract the reflected beam, avoiding power losses of both incident and reflected beam and destruction of polarization. The sensitivity of our device in the reflecting scheme reaches 5 fT/Hz1/2 at 9–60 Hz, satisfying the need to measure the human MEG/MCG or search for the fifth force. Our research paves the way for developing the compact SERF AM for multiple future applications.
A single-beam spin-exchange relaxation-free atomic magnetometer is ultra-sensitive in the zero field, which has great potential for the detection of a magnetoencephalogram. The addition of a modulated magnetic field is an important approach to achieve high sensitivity for devices of this kind. In this study, we discovered that the amplitude and frequency of the modulated magnetic field (modulation index 0–3) both influence the light absorption. We defined this effect into a function by combining theoretical analysis and the results of experiments. It is discovered that the transmission intensity decreases with an increase in the modulation index. This effect is weakened under the application of a high modulation index. In addition, the transmission intensity and bias magnetic field no longer follow a strict Lorentz curve, while a high degree of fit can be achieved by applying the numerical solution of the Bloch function. A compact magnetometer with a volume of 10 cm3 and a sensitivity of 20 fT/Hz is developed based on the single beam scheme for the proof of concept. Our study is crucial in two aspects: (1) Obtaining high sensitivity through a short measurement period and (2) alignment of the scale factor of the individual magnetometer in a detection array, which further pave the way for improvement in a magnetometer’s performance under a variety of optics platforms.
In recent years, arrayed atomic magnetometers have been continuously applied in biomagnetic scenarios. However, the crosstalk between adjacent sensors introduced by the modulated magnetic fields significantly compromises the imaging accuracy of arrayed atomic magnetometers. To solve this problem, a detuned square-wave optical modulation zero-field atomic magnetometer configuration is developed and we provide an analytical solution of this method. In this scheme, the circularly polarized pump light is used to polarize alkali metal atoms longitudinally, and a beam of detuned square-wave modulated circularly polarized light is applied transversely to generate a light-shift modulation instead of the coil-generated modulated magnetic field. Then the transverse magnetic field is measured by the optical absorption method of longitudinally circularly polarized pump light. This scheme maintains the inherent advantage of high sensitivity in spinexchange relaxation-free (SERF) atomic magnetometers. Additionally, the all-optical configuration eliminates the need for additional modulated magnetic fields or radio frequency (RF) fields, thereby mitigating crosstalk issues associated with modulated magnetic fields in array applications. Consequently, this scheme exhibits great potential for arraying and is expected to be employed in magnetocardiography (MCG) and magnetoencephalography (MEG).